Sorry, don't know the answer and doubt actually there's one. I'm pretty convinced this is no font but a custom lettering by Anthony Forster himself.
Reminds me of Thalia though. There are also Mikado/OPTI Miyako/Scriptorium Cipango/Solotype Emperor without being any of them of course... May be they inspired him to create this lettering...
Another one: Letterhead by Coffee Bin